1. Field of the Invention
The invention relates to the field of temperature-indicating compositions and devices therefor, and in particular, the sub-fields of disposable thermometers and compositions of matter which change characteristics with change in phases for use in disposable thermometers.
2. Description of the Prior Art
For many years the conventional mercury thermometer has been the primary temperature-indicating device which has been used in clinical applications for the measurement of temperature in the human body and other animal bodies, and for the measurement of temperature of gases, liquids, and even solids in commercial and industrial applications. However, as will be readily discerned by the observer, this type of thermometer has numerous disadvantages inherent in the nature of mercury, a poisonous substance to humans and other animals, and construction of the mercury thermometer with the placement of mercury within fragile glass. First, in clinical applications involving humans and other animals, several minutes, usually at least three, are required to obtain a meaningful temperature reading. Second, once used, the conventional mercury thermometer because of its extraordinary expense must be sterilized before the next clinical application. Such sterilization and resterilization often involve substantial labor costs, whether in hospitals, physicians' offices, homes, or in the field. Third, in hospital use, inevitable human error in the sterilization of thermometers presents the ever-occurring substantial probabilities of outbreaks of contagious diseases such as hepatitis. Fourth, the breakable nature of the mercury thermometer is an ever-present danger when considering the poisonous nature of mercury, especially in the presence of children. Fifth, in industrial applications, especially involving the determination of relatively high temperatures in vessels located in plants and refineries, the user must ordinarily reach into inexcessible places to locate the thermometer, and because of the extreme difference between said relatively high temperatures and the outside ambient temperature, readings from conventional thermometers are often in extreme error seconds after the withdrawal of the mercury thermometer.
Accordingly, for many years persons have attempted to construct an inexpensive device of mixtures or materials of any kind which would change in some characteristic visible to the naked eye at substantially the temperature to be measured so that the inconveniences of the conventional mercury thermometer could be avoided. For instance, Ramsden in British Pat. No. '3640 (1897) provided a piece of paper, celluloid, metal or other suitable material which would be (1) coated with, or (2) formed with a hollow or recess containing a substance, mixture of material which would change in opacity at the temperature for the indication of which the appliance is intended to be used (see page 1, lines 24-38; page 5, lines 23-45 of '3640). Ramsden desired a substance or material (see page 2, lines 9-23) that would change in color at the predetermined temperature, but did not indicate any in his specification; he only indicated several substances, generally fatty acids, which would change in opacity or change from being opaque to transparent upon change in phases from solid to liquid or vice versa (see page 3, lines 11-18), so that indicator layers, dyes, etc., would have to be employed in the device.
After Ramsden, the art primarily pursued only those heat-sensitive substances which would change from being opaque to transparent at the phase interface in devices (hereinafter described as "opaque thermometers") that would employ indicator layers having dyes that would only be apparent when the heat-sensitive substance had changed from opaque to transparent and would mix with the heat-sensitive compounds upon a change in phases. For example, U.S. Pat. No. 3,175,401 issued to Geldmacher (1965) describes a thermometer with several cavities, each containing a different thermally-indicating composition melting at a different temperature range. Each of the thermally-indicating compositions employed by Geldmacher is normally opaque below a certain temperature and transparent above a certain temperature, similar to Ramsden's compositions of matter. The temperature indication is obtained by a complete change of state of the thermally responsive material in each cavity. Furthermore, as many as forty to fifty different chemical compounds would be necessary to cover the desired human clinical temperature range of 96.degree. F. to 105.degree. F., so that Geldmacher's device was prohibitively expensive to manufacture for mass consumer use; likewise, the availability of these compounds at 0.2.degree. F. or 0.1.degree. C. increments was not disclosed.
Another type of temperature indicating device was disclosed in U.S. Pat. No. 3,465,590 (1969) to Kluth, et al. The teaching describes a thermometer which is disposable after a single application and does not employ mercury as the thermally responsive substance. Rather, Kluth, et al., employed mixtures of certain of the even series of saturated fatty acids, [perhaps] suggested by the Ramsden materials on page 3, lines 11-18 of '3640), to wit, myristic acid, palmitic acid and lauric acid for indication of temperature of the human body within plus or minus 1/2.degree. F. Again, as in Geldmacher, the device of Kluth measured and indicated temperature by a complete change of state of the thermally-responsive material in each cavity. Although the use of Kluth's thermometer obviated some of the deficiences of the conventional mercury thermometer, its application was limited to temperature measurements in the range of about 96.degree. F. to about 101.degree. F., and the accuracy was restricted explicitly in Kluth to plus or minus 1/2.degree. F., thus precluding Kluth from use for more precise the temperature measurements and replacement of the conventional mercury thermometer. As a practical matter, such Kluth instruments did not provide accurate clinical information regarding the temperature of the human or animal body during a period of fever when the temperature was frequently above 101.degree. F., as the human body is often (102.degree. F.-105.degree. F.) during high fevers. Another difficulty with the Kluth thermometer was that an accurate temperature determination really depended on a complete change of state of the solid solution employed as the thermally-responsive material. While Kluth intended for each cavity in his thermometer to have three stages of melting (each stage represented an indication of plus or minus 1/2.degree. F.), some experience by the user were necessary in order to determine which stage a cavity was in if it was melting. More probably, if the cavity responding to the closest temperature of the human or animal body to be measured did not completely change state, certain nucleation sites remained in the cavity so that the cavity rapidly solidified, causing an inaccurate measurement as withdrawal of the thermometer was followed by quick solidification of the cavities only partially liquified or containing appreciable nucleation sites because of impurities, etc. The complete change of state necessary, i.e., from opaque solid to translucent liquid, in addition to the inherent 1/2.degree. F. inaccuracy and the 101.degree. F. limitation of the device made the Kluth thermometer inadequate to replace the conventional mercury thermometer (admitted by Kluth in Column 2, lines 70-73 and Column 3, lines 1-8 of U.S. Pat. No. 3,465,590).
Still another type of thermometer was described by Finklestein in U.S. Pat. No. 3,521,489 (1970). The temperature indication in this type of thermometer is based upon the flow of a melted material from so-called "holding compartment" into a so-called "flow-inducing receiving element" such as the adsorbent material, by a capillary action (see Column 1, lines 61-72 of '489). As in the Geldmacher patent, however, temperature indication was realized by the use of numerous different thermally responsive chemical compounds, each undergoing a complete change of state at a different predetermined temperature with a corresponding change from opaque to transparency. It was obvious once again that with the employment of any "classical" material changing from opaque to transluscent at the phase change, some indicator dye or material at the bottom of a cavity would have to be placed in order to indicate readily to the observer the change in state of the composition of matter indicating the temperature to be determined. See also Crites U.S. Pat. No. 3,580,079 (1971) which required the transparent state of the temperature responsive material to be of the same index of refraction of a roughened window in order to optically smooth the window.
As the search continued for a disposable clinical thermometer to replace the conventional mercury thermometer, Weinstein and Sagi in U.S. Pat. No. 3,631,720 disclosed a specific device employing a carrier sheet (11 in '720) with a plurality of individual temperature-indicating elements distributed over at least one surface of the carrier sheet in the form of a grid with the elements buried in a corresponding number of cavities (located between the sheet 11 and surfaces 20A and 10A), each element 12 having an opaque layer covering an indicator element 20. Upon melting of the coatings 22 in '720, the indicator material 20 would be exposed to the observer. The drawback of '720 was that the manufacturer of a multilayered device as shown in FIG. 4 of '720 with a "sandwich" indicator means 20 in temperature-indicating elements 12 became expensive.
In U.S. Pat. No. 3,946,612 (1976) to Sagi and Weinstein, the specification disclosed the use of a heat conducting carrier having a plurality of spaced cavities with a corresponding plurality of solid solutions each comprising an organic layer of at least two different organic chemicals (ortho-chloronitrobromobenzene and ortho-bromonitrobromobenzene) in varied composition ratios deposited in said cavities that would turn from opaque to clear upon a change in phase from solid to liquid. This organic layer (9 in '612) formed a sandwich for an indicator layer (13 in '612) between it and a masking or opaque layer (15 in a multilayered device similar to U.S. Pat. No. 3,665,770). When the cavity of FIG. 2 of '612 was heated to a predetermined temperature, the composition of matter would change from a solid to a liquid state, permeating the indicator 13 and forcing a dye into the opaque layer to change the color of said opaque layer to the color of the dye. Several problems were presented in the construction of the '612 multilayered device: first, such a device with three internal layers in the cavity and two transparent external layers was hard to manufacture and very expensive. Second, sometimes the organic composition would not totally change from liquid to solid, so that nucleation sites remained in the organic layer 9; hence, resolidification quickly occurred upon withdrawal of the thermometer, and not all the dye was forced into the upper or opaque layer 15. Third, because of the size of the layers, it was sometimes hard to visualize the change in color when only some of the dye was transferred into the previously opague layer. For other examples of "opaque" thermometers, see Keele, U.S. Pat. No. 3,859,856 (with "supercoolable" inorganic compounds, column 4, lines 50-54); Loconti, U.S. Pat. No. 2,928,791 (dyes employed with solvents of Table I); Gignilliat III, U.S. Pat. No. 3,430,491 (physical movement of heat-sensitive solvent upon melting into "absorbent backing" layer with different color, column 7, lines 54-59); Roszkowski, U.S. Pat. No. 3,785,336 (methyl sterate); Godsey, Jr., U.S. Pat. No. 3,980,581 ("nucleating" agents to limit or reduce undercooling); Wahl, et al., U.S. Pat. No. 3,002,385; Fryar U.S. Pat. No. 3,597,976; Lang, U.S. Pat. No. 3,677,088 ("spacer layer" between indicator layer and heat-sensitive material); Pickett, U.S. Pat. No. 3,704,985 (ortho-chloronitrobenzene:ortho-bromonitrobenzene heat-sensitive material, but no "space layer"); Chadha, U.S. Pat. No. 3,712,141 ("space layer"); Pickett, U.S. Pat. No. 3,765,243 ("self-firing thermometer" with exothermic reaction between heat-sensitive material and dye); Godsey, U.S. Pat. No. 3,774,450 ("frangible" spacer layer to be crushed before application); Pickett, U.S. Pat. No. 3,826,141; Ayres, U.S. Pat. No. 3,922,917 (avoids "cover" layer by means of crushable dome); Pecorella, U.S. Pat. No. 3,929,021; Chadha, U.S. Pat. No. 3,956,153; Sagi, U.S. Pat. No. 3,835,990, Keele, U.S. Pat. No. 3,859,856; Sagi et al., U.S. Pat. No. De. 238,661 (1976); Nollen, U.S. Pat. No. 3,895,523; Chilton, U.S. Pat. No. 3,998,098; and Pickett, U.S. Pat. No. 3,871,232.
The phenomena of undercooling encountered with various heat responsive materials in passing from liquid to solid is taught in Chadha, U.S. Pat. No. 3,956,153 to be minimized by incorporation of predetermined amounts of a regenerative nucleating agent partially or wholly soluble in some degree in the heat responsive materials.
Another form of device in another art and not to be confused with the "pure" thermometer (this is used only for measurement of temperature) is the "time-temperature" thermometer or "time-temperature" watch which indicates by integration of time and temperature a property of a substance (such as deterioration of meat due to elevated temperature). For example, Chapman in U.S. Pat. No. 2,195,395 teaches the measurement of the thermal abuse of frozen food by indicating whether or not a chemical reaction has proceeded past a certain point through a measurement of the change in pH, using a dye in water. A major advance in such an art was Larsson, U.S. Pat. No. 3,946,611, wherein paraformaldehyde 19 in FIG. 2 decomposes at a rate which is a function of temperature to produce formaldehyde gas that permeats through membrane 22 to contact a wick means 18 which contains hydroxyamine hydrochloride and a dye and low volatile acid. After an accumulation of time the HCl lowers the pH of wick means 18 so that the dye and wick change color (see Example 3). The color change does not indicate a change in color upon change in phases of a solvent. See also Gessler, U.S. Pat. No. 3,065,083 describing a time-temperature indicator to indicate the presence of fatty acids for frozen food packages; U.S. Pat. No. 3,437,070 to Campbell; and U.S. Pat. No. 3,479,877 to Allen.
Still another type of device in still another art and not to be confused with the "pure" thermometer is a device employing "liquid crystals"--a "liquid" which, although turning color in a specific range of temperatures (usually in a range of 11/2.degree. F.-2.degree. F. and no better than 1/2.degree. F.) because of a change in orientation of the liquid, is not suitable for thermometry because the "liquid" is incapable of supercooling, therefore resolution at better than 1/2.degree. F. is difficult and the device must be read immediately upon withdrawing the "liquid crystal" device from the subject. Examples of "liquid crystal" devices and sprays and related technology are Sanford, U.S. Pat. No. 3,633,425; Flam, U.S. Pat. No. 3,661,142 (accuracy only within 2.degree. C.); Parker, U.S. Pat. No. 3,898,354; Suzuki, U.S. Pat. No. 3,974,317; and Davis, U.S. Pat. No. 3,619,254.
A state of the art method for depositing precisely metered quantities of liquid on a small surface is revealed in Pickett et al., U.S. Pat. No. 3,810,779.
Japanese Patent Applications Nos. 47-34735 and 50-105555 show, respectively, compositions (1) comprising a dye and an acid with a polymeric material, and (2) a dye, an acidic compound, and a solvent which change colors although not at the melting point of the solvent.
Some abbreviated attempts have been made to find substances that would change color upon change in phases for use in thermometers, but none have been able to overcome the combined problems of employing many different unrelated compounds, accidental overheating, etc. For example, Jennings in U.S. Pat. No. 2,261,473 combines certain cognizable, organic dyes (page 2, column 2, lines 13-28) with certain solvents (page 2, column 1, lines 56-60) wherein the change in pH changes the color of the dyes, but needs, like Kluth, 45 or 50 different compositions over a range such as the human clinical range. A major advance in the art is Renbaum, U.S. Pat. No. 3,700,603 wherein no solvent system is employed, but the organic moieties ("electron donors" and "electron acceptors") do change color upon change in phases (see Table I, columns 5 and 6). However, because Renbaum apparently did not attempt to find a suitable solvent system for his electron donor-acceptor pairs, a number of different parts would be needed for almost any temperature range to be determined, e.g., the same problems as Kluth appeared. See also Hammond, U.S. Pat. No. 3,576,604, who also does not use a solvent over a range of temperatures.
An inexpensive disposable thermometer was needed and intensely desired in the thermometer industry which would be easily constructed and have materials which would change some characteristics visible to the naked eye but not readily susceptible to quick reversibility upon withdrawal from the source whose temperature was to be measured. If one could provide a chemical substance that would change in color in and of itself upon change in phases, the use of dyes in indicator layers would be eliminated. Likewise, a disposable thermometer was needed to magnify the presence of an indicator layer in cases involving "classical" substances that changed only from opaque to transparent upon change in phase from solid to liquid.